Just as a real number can be rational or irrational, a complex number can be real or imaginary. Any complex number that is not real is imaginary. For example, 5 + 2i is imaginary and complex, just as 1/2 is rational and real. However, 5 + 2i is not "pure imaginary", as a pure imaginary number must in the form bi (or 0+bi) with b not equal to 0.